special situation——两个short型变量相加超出short的表示范围
short型所能表示的数的个数为（32位机器）：2^16 = 65536。若为unsigned short表示范围为：0到65535。若为有符号的，表示范围为：-32768到32767，当为32767时，符号位为0，其余15位为1；当为-32767时，符号位为1，其余15位为1；因为是有符号数，所以有正0和负0之分，负零用于表示-32768。
下面是一段测试程序，通过输出结果可以看出这个special situation的处理情况。
1 #include <iostream>
2 #include <fstream>
3 #include <cstdlib>
4
5 using namespace std;
6 int main(int argc, char *argv[])
7 {
8 short s1 = 32767;
9 short s2 = 1;
10 cout << "s1 = " << s1
11 << " s2 = " << s2
12 << endl;
13 short sum = s1 + s2;
14 cout << "Sum of s1 and s2 is " << sum << endl;
15
16 s1 = sum - s2;
17 cout << "Is s1 is as the old value? s1 = " << s1 << endl;
18 system("pause");
19 return 0;
20 }
21
2 #include <fstream>
3 #include <cstdlib>
4
5 using namespace std;
6 int main(int argc, char *argv[])
7 {
8 short s1 = 32767;
9 short s2 = 1;
10 cout << "s1 = " << s1
11 << " s2 = " << s2
12 << endl;
13 short sum = s1 + s2;
14 cout << "Sum of s1 and s2 is " << sum << endl;
15
16 s1 = sum - s2;
17 cout << "Is s1 is as the old value? s1 = " << s1 << endl;
18 system("pause");
19 return 0;
20 }
21
s1=32767
s1=32768
s1=32769
s1=32770
如果不明白的话，可以参考这个随笔“原码、反码、补码，计算机中负数的表示”http://www.cnblogs.com/younes/archive/2009/11/13/1602253.html
